Electronic telegraph repeater



T. L. WALTERS ELECTRONIC TELEGRAPH REPEATER July 24, 1951 F/G/ v1? Sheets-Sheet 1 Filed Jan. 15, 1948 Eil/6 gil/7 T. L. WALTERS ELECTRONIC TELEGRAPH REPEATER July 24, 1951 2 sheets-sheet 2 Filed Jan. 15, 194s .wml

MEAN,

Attorney Patented July 24, 1951 ELECTRONIC TELEGRAPH REPEATER Trevor Lyndon Walters, Kenton, Harrow, England, assignor to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application January 15, 194.8, Serial No. 2,354 In Great Britain January 16, 1947 This invention relates to electronic repeaters for teleprinter signals.

The object of the invention is to provide an arrangement that Will receive badly distorted signals and automatically transmit corresponding signals re-shaped into nearly perfect form.

Regenerative repeaters for this purpose have previously been proposed in which an oscillator for timing the reception and retransmission of each signal element has been started into oscillation on receipt of the start element of4 a signal. It is, however, difficult to ensure that such an oscillator shall bc started up Without appreciable delay and if such delay occurs, the timing of the separate elements of the signal and the consequent perfect re-shaping of those elements cannot be properly carried out.

Oscillators that maintain their frequency with high precision cannot be relied upon to start up suddenly, and conversely oscillators that can be relied upon to start up when required, do not maintain a high precision of frequency.

According to one feature of the present invention, a regenerative repeater for teleprinter signals, comprises an oscillator for timing the reception and retransmission of each signal element and means jointly under the control of the start element of a signal and of a free `running oscillator having a frequency that is a multiple of the frequency of the first-mentioned oscillator for starting said rst-mentioned oscillator into oscillation and controlling its frequency.

The free-running oscillator thus controls the frequency of the timing oscillator and preferably it does so by means of at least two stages of frequency subdivision. Preferably also an oscillator for timing the whole period of the signal is also controlled from the free-running oscillator by means of at least two stages of frequency subdivision.

In the embodiment to be described for a socalled '71,(2 unit code, i. e. a code having 'a start element and live code elements all of unit length and a stop element of 11/2 units length, the period of the oscillator timing the signal is made equal to '7 unit lengths, for a reason that will be eX- plained hereinafter. For the usual signalling speed of 50 bands, the oscillator timing the signal elements has a frequency of 50c. p. s. and. this is controlled from a free-running oscillator of a frequency of 2,500 c. p. s. through intermediate oscillators of 500 and 100 c. p. s. respectively. Similarly the oscillator of 7 unit period, i. e. of '7l/7 c. p. s. is controlled from an oscillator of 142/7 c. p. s. which in turn is controlled by the oscillator of 10D c. p. s.

According to another feature of the present invention a regenerative repeater for teleprinter signals comprises electronic oscillator means, Wholly electronic` means for starting up the said oscillator means, means controlled from said oscillator means for timing the signal and separate elements of the signal, and Wholly electronic means for regenerating the signals under control of said timing means and for repeating the regenerated signals. In this Way delays and imperfections due to the use of contact-making relays are avoided. i

An embodiment of the invention will now be described with reference to the accompanying drawings, in which Fig. 1 shows the circuits of a regenerative repeater for a start-stop 5-unit code, and

Fig. 2 shows the relative phases of the anode voltages of certain time base oscillators of Fig. 1 to the incoming signal.

Referring to Fig. 1, thermionic valves (pentodes) V1, V2, Vs, V4 and V5 constitute saw-tooth oscillators of a known kind, the circuit constants being so dimensioned that the respective natural frequencies are 500, 100, 142/1, 'Z1/7,` and 50 c. p. s. The oscillator V1 is driven from a free-running oscillator (not shown) of 2500 c. p. s. which is controlled to the required degree of accuracy of frequency, the drive being by means of a connection at the point D in known manner. In the condition when no signals are being received the grids of the valves VI. V5 are biassed to cutoff, and the anode condensers are therefore in charged condition, being connected between positive of the I-I. T. supply and earth. During operation oscillator V1 controls oscillator V2 and oscillator V2 controls oscillators Vs and V5, whilst `oscillator V3 controls oscillator V4.

The input signals are applied to the grids of valves V6 and Vl and also to the grids of valves VH and V12 over the lines L-l and L-2. A valve V8 is coupled to valve V1 to form a 'trigger circuit. Other pairs of valves V9, Vl and V14, VIE also form respective trigger circuits. When no signals are being received, or when a continuous marking condition is applied to the line theleft-hand valves V1, V9 or V14 will render them non-conducting and cause the right-hand valves VB, Vl and VI5 respectively to become conducting. The action is such that subsequent reversals of the signal potentials applied to the 1.Jgrids of the left-hand valves Will not reverse tive potentialis applied `over wireLZ'to Vthe gridv of valve. Vl and negative potential is applied.

overwire Li to the grid of valve V5, such potentials emanating from the distant transmitter'-v` nal is received these potentials arev reversed-as:`

is well known in the polar system,.of..transmisz sion, and valve V1 is rendered".non*conducting;` I

and V6 becomes conducting. The anode potential of V5 drops, thus reducingf the` screen-grid.

potential of V7. This assists in keeping valvegVl'! non-conducting. The other valve V8` of the trigger pair V7 and VS becomes conductingandthe rise in potential of the control grid of valve Vdi? is' applieda-to` the control grids: ofi Valves Vli Vl'i' and theyf. commence tonoperate; generating. saw?y toothy wave forms. ning oscillator'.'controlling .the operation't of V l is; as assumed above, of a freduencyroffc. p..- s. then thernaximurn diierence betweenthej. re-

milliseconds. starts: to operateV the corresponding condenser discharges` thusfprodu'cing a` suddenzfall of potential of the anode of the correspondingvalve'..

WhenfVZ starts itsoperation, therefore,l anegative pulsewillbe transmitted from the anode-:oi-l V2 to the suppressor grid of valveV9; tendingtox rendercthatvalvenon-conducting, but a simu1- taneous positive pulse from' the'cathode; of V43-I If'y the' frees-ruhry throughthef rectifier W2: tok the control grid: ci n The wave forms at the anode of. V2; is shown:

inline BiofFig: 2*.' Orr-the occurrence 'of .thesecondnegative'pulsefrom the anode, whch'is also.vr

appliedto the-suppressor grid of valve-V9; this lastfmentioned valve is rendered rnoir-conducting,` as the cathode current of valve Vdsv nowK steady andrtherelisz'no pulsei on'the control vgriclo` valve@ V9 to vnullify the` effect of the negativefpulsedee previous paragraph' hereof:

valverV2: The wavev form at the.A anodefofzVE., whichoperates at 50` c; p. s; isV shownA in linefCof Fig. 2, and it will'be' seenthat itprovid'es Va sud-'- den falloftpotentia'l atanintervaliof lll-'ms after the; commencement of the; start element and atj intervalsof` 20 ms. thereafter, i. e. at the centrel off each' subsequent. signal element period.. Posietivepulses at. these-v intervals there-foreA occur'a-t` the screen'gridf. of' ValverV and these; positiver pulses are-:applied to the?. screen grids of? valvesz'` Vl'l and Vl2, thusI momentarily rendering; bot-h1.

these valves conducting. Thea-bias normally ap'- plied to thecOntrol grids of; these'y valves, inthe absence'offany incoming signalswould make both' valves non conducting. Ifl howeverthe incoming. signal applies positive potential overLl, then'- atth'eiinstantVi l becomes conducting lbecause ofi the pulse from the valve V5, a negative pulse from the anode. ofv valve VH is applied` to' the'v suppressorv grid of "valves Vl'lland this valve be comes non-conducting, valve.l VI'5, becomescorrducting. If on the other hand the incoming signal is applying positive potential over L2 then, Vit becomes momentarily conducting on the application of the pulse from valve V5, and a positivepulse frornthe cathode. of valve V12 is applied' tothe control grid-of valve Ill and vvalve V14 remains conducting. In this manner the trigger circuit VM, V|5 is made to follow the sign of the input. signal. If the valve Vit is conducting, valve'Vl is non-conducting and vice versa. The terminals of the outgoingline are L3 and L and the signalsfsentiover this line will be a replica offth'ose receivedtover line Li L2 but delayed by l0 ms.

At the end oa .signal interval the circuit must be. reset toloe ready to receive another signal. The re-setting is performed by means of the tube V45 The circuit of this tube has a period ci ms., as shown in line E of Fig. 2. At the end of: this period the anode becomes suddenly negative and the suppressor grid'positive. The posi tive pulse from the suppressor grid of Vit is appliedrto` the control grid of V53, normally biased to cutoff: Valve W3 becomes conducting and the anode lthereof drops in potential, and since the anode potential is. applied tothe screen grids 'of valveslV-S" and Vit-these valves oi the respective trigger pairs viz.

from the trigger pair Vl, V3.

It should be noted that, althoughA the anode;v

ofi Vfl: becomes suddenly negative at the comu menceinent of operations, i. e. the receipt of a start element of a signal, the consequent positivevpulse from the suppressor grid does not at that'time cause valve VVIS to become conducting i since its control grid is kept highly negati-ve fromthe V9;- Vl ii trigger circuit.

Rectiers--Wl and'VIi arranged between the cath'odecircuit ofv valve Vt and the grid circuit of'fvalveyVQ' prevent any negative signal being' passedfrcm the former to they latter which would oppose `"J9-being rendered conducting;

At the moment at which the circuit is reset, a stop.y element will have been transmitted for lilfrns., so'that` even if the next start elementaithe. received; signal commences imn'lediatelyjbecauseitoccurs early by the maximum possible periodi; e. 1/2 a signal' element, the stop. clement will continue to'be transmitted toA line L3, he fora'affurther'. if). ms. so that'a minimum of 20ans. stop signal .is always transmitted.

The anodef condensers of the valve Vl-Vlwillcommence-to charge up when these valves are made, non-conducting by the triggerv pair. Vi, Vt. It astart2 element 'oereceived', the initial large pulse of positive on the control grids due tothey condenser-between the anodeof tube'Vl and the gri-drof tube V8; willensure the discharge of the anodezoondensers and the restarting oi the saw toothvoscillations in phase. The condensers of thecircuit.` of valve V5 will have the full period of- 20rms. in which to charge' so that the-puise obtained by thev discharge of this condenser inV the"'middleoi the of full amplitude;

1;. Inzan apparatus for regenerating signal our# rents'in an equal-unit-code telegraph system oi the polar transmission type, an. input circuit adapted to' receive distorted signal currents of either polarity in a code of equal-units at'random combinations, two` electrically; associated.

VT! and V9 being restored to`4 theirforignal conducting conditions. The gridA potential of. Valves Vi. V5v is reduced to a point atfwhicl'i` theybeconienonfconducting by the biasA start element received will be sawtooth oscillator circuits a source oi regularly recurring pulses, having a repetition rate of a multiple of said oscillator circuits, said source coupled to said oscillator circuits and adapted to cause the operation thereof, an output circuit, means electrically associated with said output circuit for Xing under operation by said random combinations the period of duration and the polarity of each of said units in said output cirm cuit by the full period length of the first one of said oscillator circuits, means for iixing the period of the sum of the total said units of a single operation in said output circuit by the whole period length of the second ci said oscillator circuits.

2. In an apparatus for regenerating currents representing signal characters inan equal-unitcode telegraph system of the polar transmission type over an outgoing line from signal currents received over an incoming line, comprising an input circuit to receive code signals of either polarity of equal units at random combinations, a first sawtcoth oscillatory circuit having a period equal to a single unit length of said code to regenerate the period of the units of said signals, a second sawtooth oscillatory circuit having a period equal substantially to the length of the sum of all the units and fractions thereof, in the code employed to regenerate the period of a complete codecharacter operation, a source of regularly recurring pulses, having a repetition rate of a multiple of said oscillator circuits, said source coupled to said oscillator circuits and adapted to cause the operation thereof, and means electrically coupling said two oscillatory circuits to each other and to said input circuit, whereby said periods are coordinated.

3. In an apparatus for regenerating currents representing signal characters as claimed in claim 2, wherein said rst oscillatory circuit is normally inoperative, said rst circuit responsive after a given delay to the receipt of the first unit of said code combination by said input circuit, and operable after said delay to produce sawtooth waves having a period equal to that of a single unit length of said code.

4. In an apparatus for regenerating currents representing signal characters as claimed in claim 2, further comprising a third sawtooth oscillatory circuit having a period less than that of a single unit length of said code and responsive to the receipt of the rst unit of said code combination by said input circuit, for delaying operation of said first savvtooth oscillatory circuit.

5. In an apparatus for regenerating currents representing signal characters as claimed in claim 2, wherein said input circuit comprises a 5 Number 6 plurality ci thermionic valves, each having a cathode, an anode and a control electrode, the control electrodes of each of said valves connected to an incoming line, each of said valves, adapted to conduct upon the receipt of a posi-- tive incoming signal element.

6. In an apparatus for regenerating currents representing signal characters as claimed in claim 2, wherein said input circuit further coniprises a pair` i thermionic valves each having control electrodes, an anode and a cathode, corresponding of the control electrodes of said valves connected in opposite sense to the incoming line, means for applying an impulse to corresponding electrcdes of each of said valves from said first oscillatory circuit for timing the reception of each. signal element, said valves having sufficient bias thereon to prevent conduction eXn cept upon the simultaneous receipt of one of impulses from said oscillatory circuit and of a positive incoming signal element, and means to apply oppositely poled impulses for retransmitting a signal of a sign corresponding to the received incoming signal elements, upon one of said valves becoming conducting.

7. Inran apparatus for regenerating currents representing signal characters as claimed in claim 2, further comprising a third sawtooth oscillatory circuit, said nrst oscillatory circuit being normally inoperative, means for causing said iirst oscillatory circuit to operate after aigiven delay, said means comprising a control device having two input circuits, means for applying said code signal units and the output of said third oscillatory circuit to separate of the input circuits of said control device, said control device responsive to input application of said third oscillatory circuit output alone for causing said first oscillatory circuit to operate.

8. In an apparatus for regenerating currents `representing signal characters as claimed in claim 7, wherein said received code signal units arediierentiated before application to said input circuit and the output of said third oscillatory circuit, the output of said third oscillatory circuit having substantially twice the period of a unit of said code signal.

TREVOR LYNDON WALTERS.

REFERENCES CITED The following references are of recordin the file of this patent:

UNITED STATES PATENTS Name Date Morrison Aug. 20, 1946 Pelle c June 28, 1949 

